The entire disclosure of Japanese Patent Application No. 2010-075008, filed Mar. 29, 2010 is expressly incorporated by reference herein.
1. Technical Field
The invention relates to photodetector devices, photo sensors and spectrum sensors.
2. Related Art
A known photodetector device is composed of a photodiode having a first semiconductor region of a first conductivity type (for example, N type) formed on a substrate, and a second semiconductor region of a second conductivity type (for example, P type) formed on the first semiconductor region.
For example, Japanese patent 3584196 (see claim 1, FIGS. 1, 5 and 11, and Paragraph 0062) (Patent Document) describes a photodetector device having (1) a first semiconductor region of a first conductivity type, (2) a second semiconductor region of a second conductivity type arranged on the first semiconductor region, (3) a third semiconductor region of the first conductivity type arranged on the surface of the second semiconductor region, (4) an electrode region of the second conductivity type that is arranged on the surface of the second semiconductor region and connected to an anode or a cathode, wherein the third semiconductor region is formed in a manner to surround the periphery of the electrode region, and the electrode region has an impurity concentration higher than that of the second semiconductor region. According to the Patent Document, the impurity concentration of the third semiconductor region is made higher than the impurity concentration of the second semiconductor region, whereby the capacitance of the photodetector section is lowered.
However, in the photodetector device described in the Patent Document, because the impurity concentration of the electrode region is made higher than the impurity concentration of the second semiconductor region, and the impurity concentration of the third semiconductor region is made higher than the impurity concentration of the second semiconductor region, the impurity concentration of the second semiconductor region has to be made relatively low. On the other hand, in order for carriers (electrons or holes) generated by the photoelectric effect in the second semiconductor region of the second conductivity type that forms a PN junction with the first semiconductor region of the first conductivity type to move into the electrode region of the second conductivity type, the carriers need to move within the second semiconductor region of the second conductivity type. When the impurity concentration of the second semiconductor region is lowered, as described in the Patent Document, the electrical resistance of the second semiconductor region becomes higher.